first build attempt

shaders/graticule.vert

@@ -0,0 +1,26 @@
+/*
+ * MIT License
+ * Author: Mark Allyn
+ *
+ * graticule.vert — vertex shader for the incandescent bearing graticule,
+ * the yellow cursor, and any other 2-D screen-space line geometry.
+ *
+ * Vertices are supplied in window pixels (origin top-left, y down).
+ * The shader converts them to OpenGL NDC (origin bottom-left, y up).
+ */
+#version 330 core
+
+layout(location = 0) in vec2 aPos;   // screen pixels, top-left origin
+
+uniform vec2 u_viewportSize;         // (WINDOW_WIDTH, WINDOW_HEIGHT)
+
+void main() {
+    // Convert: pixel → NDC
+    // ndc.x: 0 → -1, width → +1
+    // ndc.y: 0 → +1 (top), height → -1 (bottom)
+    vec2 ndc = vec2(
+         aPos.x / u_viewportSize.x * 2.0 - 1.0,
+        -aPos.y / u_viewportSize.y * 2.0 + 1.0
+    );
+    gl_Position = vec4(ndc, 0.0, 1.0);
+}